How would Data have been able to do that? Data couldn't get close to Fajo because of the proximity-actuated field.
He already tried numerous other forms of resistance throughout the episode, and this was his only chance to get ahold of the disrupter.
It's a fair point about the field, I'd forgotten about that. But he already has the disrupter, we're past that bit, aren't we? He might try to locate another weapon - one that can incapacitate from a distance as opposed to only
being lethal - and work from there. He could warn Fajo's employees that Fajo plans to use them as ransom fodder to manipulate him and see if he can get one of them to assist him. He could even promise them that they can help themselves to some of Fajo's wealth if they help Data to bring Fajo to justice.
I suppose if Data truly thinks that none
of those are viable options, he can shoot.
Though as I say, for dramatic purposes I've no problem with how it played out.